1. Field of the Invention
The present disclosure relates to semiconductor devices, and more particularly to a method for forming a top oxide with a nitride liner.
2. Discussion of Prior Art
Semiconductor memory devices such as dynamic random access memories (DRAM) typically include memory cells. These memory cells comprise storage nodes. These storage nodes can be formed within deep trenches etched into substrate of a semiconductor memory chip. The storage nodes can be accessed using an access transistor, which allows a charge to be stored in the storage node or retrieved from the storage node depending on a desired action, e.g., a read function or a write function. Electrical isolation of the storage node from a gate conductor can be important to the performance of the device.
A top trench oxide layer formed over the storage node provides electrical isolation between the storage node and gate conductor. Each storage node typically includes a polysilicon material that partially fills the deep trench. During fabrication of the device, a recess can be formed at the top of the trench. An oxide, for example, silicon oxide, can be formed over the device including the polysilicon in the trench. Portions of the deposited oxide can be removed by planarizing the surface of the device and by recessing the oxide to leave an oxide layer at the bottom of the recess, for example, 5–50 nm of material. This oxide layer is referred to as a trench top oxide or isolation.
Similar to the trench top oxide, a top oxide for vertical transistors provides electrical isolation. The top oxide isolates the gate conductor from the substrate. An electrical connection can be formed between the gate conductor wiring layer on the wafer surface and the vertical gate conductor in the trench. Methods for forming the top oxide typically involve complex process flows, which can add to the cost of manufacturing the DRAM devices. In addition, exposed arrays during processing can result in irregularities in the DRAM device affecting device performance.
Therefore, a need exists for a method for structuring a top oxide with a nitride liner having a reduced number of process steps and a protected stud during processing.